Independent party tribunals (i.e. intra-party courts) can be used by both the party leadership (e.g. to discipline members) and rank-and-file members (e.g. to challenge the leadership overstepping its authority). Thus, their study offers broad insights into party conflict regulation we know little about. Integrating the literatures on party organization, intra-party democracy and judicial politics, we propose two theoretical rationales to account for tribunal decision-making (whether a case finds tribunal support): tribunal decision-making can be theorized as shaped by elite-member divisions or, alternatively, by how verdicts affect the tribunal’s own position in the organization and organizational stability generally. We test hypotheses derived from these rationales using a new data set covering 243 tribunal decisions made over the life spans of three German parties. While both rationales are empirically relevant, the ‘organizational stability rationale’ proves particularly insightful.